1. Field of the Invention
This invention relates to emergency vehicle control systems for providing warnings of approaching emergency vehicles at intersections and more particularly relates to an emergency vehicle control system that utilizes traffic loop for preemption of traffic signals at an intersection.
2. Background Information
Using existing technology current traffic loops are normally used to detect the presence of cars at an intersection. These traffic loop detectors activate and control the operation of traffic lights at intersections according to the approach of vehicles.
In the past decade, several approaches have been taken to provide traffic signal preemption for emergency vehicles. Existing systems use strobe lights to activate optical receivers at an intersection. Other systems use noise pattern recognition to preempt based on approaching sirens. Recent systems have been developed using Global Positioning Systems (GPS); this has shown to be very effective in light metropolitan and rural areas. However each of these systems have drawbacks.
The strobe phase preemption system has the drawback that an optical line of sight is required. Further the viewing angle of the optical receiver (problems with hills and turns) and range preemption is limited to a few hundred feet. Also the receiver units and installation in vehicles are expensive.
Noise pattern detection systems use siren noise detection and recognition for preemption. This is not advantageous because the direction of the sound is required. Also ambient noises can diminish the detection of siren noise such as traffic, horns, general traffic noises at intersections. Another drawback is that the siren noise recognition is of course severely limited by distances.
GPS based preemption systems while effective also have some drawbacks. Such systems because they are very technical inherently require very expensive equipment. The system can also have difficulties because of vehicle position (buildings, bridges, large cities, etc.) can occlude the signal. Further the system is entirely dependent upon GPS satellites and selected positioning modes.
Investigations have determined that GPS (when available) is very effective at the timing and determination of vehicle position. Original versions of software (and hardware) designed for highly accurate map-matching have precise location determination of the emergency vehicle. The timing of the pedestrian and clearing phases at an intersection was incorporated into calculations of when to start preemption at any given intersection. There was concern that GPS-based system would not be accurate enough based on the limited selected positional accuracy. However even when the selected position was still activated (at an accuracy of no more than ±50 meters), it was found the system could adapt effectively. Therefore the approach to the preemption algorithm became more of a statistical calculation rather than a precise estimated-time-to-arrival calculation. In other words, given occasional accurate positioning the system could effectively compensate for large deviation between accurate position locks.
One of the reasons the system could accept such large deviations in the system of the car was due to the appearance of normal behavior at any given intersection. When pedestrians and motorists are not aware that an intersection was preempted, they simply didn't care. As long as a traffic light was returned to normal operation within approximately two minutes, this was seemingly no awareness of any problem. Given the infrequency of an emergency vehicle passing through a given intersection throughout the day, the frequency that related delays would exceed two minutes is negligible. This allows loose margins on when to start preempting. In other words even if a system determines there is only a 50 percent probability that a vehicle is going through an intersection, it could still preempt without noticeable disruption in traffic.
It is important to note that an emergency vehicle warning system such as that disclosed and described in U.S. Pat. Nos. 4,704,610 and 4,775,865 has two components: (1) the preemption of a traffic light and (2) a visible LED sign that alerts motorists to oncoming emergency vehicles. If the LED sign is used in conjunction with the invention disclosed herein, the motorist is aware of an act of preemption. Thus, the two-minute limitation does not apply. The LED sign requires much more active positioning to avoid “false warnings” (and likewise) “late-warnings”.
In designing a preemptive system it was apparent that the system of the patents disclosed hereinabove would not function effectively in congested areas such as: large metropolitan cities, tunnels, and under bridges. When the lessons learned about accuracy are applied to the GPS limitations, it is clear that a truly effective preemption system only requires accurate vehicle positioning at critical nodes in the system (nodes being key signal equipped intersections). Between intersections, even using rough calculations based on dead reckoning, a system can produce highly effective predictions on when to preempt oncoming lights without causing unnecessary disruption in traffic flow.
Accordingly it is one object of the present invention to provide a traffic light preemption system for use in emergency vehicle warning system utilizing current traffic loops normally used to detect the presence of cars at an intersection.
Another object of the present invention is to provide a traffic signal preemption system utilizing existing traffic loops having a “car-active” system that relies on an on-board car computer to relay real-time vehicle positioning and travel information to surrounding intersections.
Still another object of the present invention is to provide a traffic light preemption system utilizing existing traffic loops that is “car-passive” and relies on road-based detection and communications to identify vehicles as they pass.